This invention relates to a reciprocating-piston type fluid translating device such as used for pumps or motors. More specifically, the invention relates to a light-weight-core piston of the type used in these units having an improved means for retaining the core against axial displacement during operating of the piston, and further having an improved core design to increase piston strength against the high stresses developed within the translating unit.
Conventionally, the weight of the pistons contained within these translating units is reduced by hollowing out the skirt portion of the pistons. This, however, increases the dead volume of fluid that must be moved within the translating unit, and can have the effect of decreasing the efficiency of these units. Consequently, it is usual to refill the hollowed-out portion with a material of lighter weight than that of the piston, and which possesses a sufficiently high bulk modulus to resist compression under the high pressures encountered during operation. Such filler material must be positively retained within the piston in some manner, so that it will not be displaced during operation of the translating units, thereby potentially causing severe damage to such units.
Prior attempts have been made to provide light-weight-core pistons for use in these hydraulic translating units. However, the means employed to retain the filler in position within the pistons are frequently elaborate and expensive, or inadequate, leading to loosening or dislodging of the core during operation of the piston, and often both disadvantages are present. Also, although prior core designs have usually resulted in a lighter-weight-piston, the ensuing reduced piston strength has occasionally caused the piston to succumb to the high stresses developed during operation.